Temperature sensor and method for production thereof

Abstract

A temperature sensor having sturdy construction is simple to install and to package, is uncomplicated to manufacture, and suitable for reliably detecting rapid temperature changes. The temperature sensor ( 1 ) includes a silicon substrate ( 2 ) in which at least one porous area ( 3 ) is formed, the degree of porosity and the thickness of the porous area ( 3 ) being chosen so that the porous area ( 3 ) is thermally isolated from the silicon substrate ( 2 ). In addition, the temperature sensor ( 1 ) includes temperature measuring elements ( 6, 7 ) for detecting the temperature difference between the silicon substrate ( 2 ) and the porous area ( 3 ). The temperature sensor may also include heating elements for testing the sensor function.

What is claimed is:  
     
         1 . A temperature sensor 
 having a silicon substrate ( 2 ) in which at least one porous area ( 3 ) is formed, the degree of porosity and the thickness of the porous area ( 3 ) being chosen so that the porous area ( 3 ) is thermally isolated from the silicon substrate ( 2 ), and    having temperature measuring elements ( 6 ,  7 ) for detecting the temperature difference between the silicon substrate ( 2 ) and the porous area ( 3 ).    
     
     
         2 . The temperature sensor as recited in  claim 1 ,  
       wherein the porous area is made up primarily of porous silicon.  
     
     
         3 . The temperature sensor as recited in  claim 1 ,  
       wherein the porous area ( 3 ) is made at least partially of silicon dioxide.  
     
     
         4 . The temperature sensor as recited in one of claims  1  through  3 ,  
       wherein the porous area ( 3 ) has a porosity of at least 60%.  
     
     
         5 . The temperature sensor as recited in one of claims  1  through  4 ,  
       wherein the porous area ( 3 ) has a thickness of approximately 10 μm to 200 μm.  
     
     
         6 . The temperature sensor as recited in one of claims  1  through  5 ,  
       wherein the porous area ( 3 ) adjoins a main surface ( 4 ) of the silicon substrate ( 2 ), and at least one protective layer ( 5 ), in particular a protective layer ( 5 ) of Si x N y , is formed at least over the porous area ( 3 ).  
     
     
         7 . The temperature sensor as recited in one of claims  1  through  6 ,  
       wherein heating elements ( 11 ) are provided for heating the porous area and for testing the sensor function.  
     
     
         8 . The temperature sensor as recited in one of claims  1  through  7 ,  
       wherein the temperature measuring elements ( 6 ,  7 ) and/or the heating elements ( 11 ) are realized in the form of resistors, which—depending on their function—are located in the area of the silicon substrate ( 2 ) and/or in the porous area ( 3 ).  
     
     
         9 . The temperature sensor as recited in  claim 8 ,  
       wherein the resistors ( 6 ,  7 ) are made of metallic materials, in particular of platinum, aluminum, or titanium.  
     
     
         10 . The temperature sensor as recited in  claim 8 ,  
       wherein the resistors are made of semiconductive materials, in particular of doped silicon or silicon-germanium.  
     
     
         11 . The temperature sensor as recited in one of claims  1  through  7 ,  
       wherein the temperature measuring elements are realized in the form of at least one thermal chain ( 21 ), each thermal chain ( 21 ) including two printed conductors ( 22 ,  23 ) of different materials that are connected to one another at two contact points ( 24 ,  25 ), the one contact point ( 24 ) being located in the area of the silicon substrate ( 2 ) and the other contact point ( 25 ) being located in the porous area ( 3 ).  
     
     
         12 . The temperature sensor as recited in  claim 11 ,  
       wherein the printed conductors of the thermal chain are made of metallic materials, in particular of platinum, aluminum, or titanium.  
     
     
         13 . The temperature sensor as recited in  claim 11 ,  
       wherein the printed conductors of the thermal chain are made of semiconductive materials, in particular of doped silicon or silicon-germanium.  
     
     
         14 . A method of producing a temperature sensor having a silicon substrate, in particular as recited in one of claims  1  through  13 ,  
       wherein at least one porous area is produced in the silicon substrate, and temperature measuring elements for measuring the temperature difference between the silicon substrate and the porous area are placed in the area of the silicon substrate and in the porous area.  
     
     
         15 . The method as recited in  claim 14 ,  
       wherein the porous area is produced in an electrochemical etching process, in particular through electrochemical anodizing using a medium containing hydrofluoric acid as the etching solution.  
     
     
         16 . The method as recited in one of claims  14  or  15 ,  
       wherein an etching mask is produced on at least one main surface of the silicon substrate, whereby the area to be etched is defined, in particular a metal mask, an n +  doping, an Si x N y  layer, or a combination of n +  doping and a Si x N y  layer being used as the etching mask.  
     
     
         17 . The method as recited in one of claims  15  or  16 ,  
       wherein the porosity produced in the etching process is determined by the doping of the silicon substrate, by the concentration of the etching solution, and/or by the current density applied during the etching process.  
     
     
         18 . The method as recited in one of claims  15  through  17 ,  
       wherein the depth of the porous area is determined by the duration of the etching process.  
     
     
         19 . The method as recited in one of claims  14  through  18 ,  
       wherein the porous silicon produced in the porous area is at least partially oxidized.  
     
     
         20 . The method as recited in one of claims  14  through  19 ,  
       wherein at least one protective layer is produced over the porous area, in particular using a CVD (chemical vapor deposition) method.  
     
     
         21 . The method as recited in one of claims  14  through  20 ,  
       wherein resistors and/or printed conductors are produced in the area of the silicon substrate and/or in the porous area by applying and structuring CVD and/or sputtered layers.  
     
     
         22 . Use of a temperature sensor as recited in one of claims  1  through  13  in connection with a motor vehicle.  
     
     
         23 . The use as recited in  claim 22  for detecting a side impact, the temperature sensor being placed in a side part of the motor vehicle which forms a largely closed hollow body, to detect the adiabatic temperature rise in the event of a side impact.